Why kick players who are lagging? The server doesn't wait for players lagging. (This isn't StarCraft or something.) It continues on. It does not cause the rest of the players to lag.
The only reason I could see is to keep poorly performing players out of the game, especially where it really matters, like in L4D, but players have the ability to vote kick. So, I don't see the point.
Lagging players are already screwed over enough. Why kick them too?
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